Interference of Known or Suspected Endometriosis in Reporting FDG PET/CT Performed in Another Indication

Endometriosis is a common gynecologic condition that may be visualized on (18)F-FDG PET/CT and mimic lesions of malignancy. We analyzed the interference of known or suspected endometriosis in reporting (18)F-FDG PET/CT performed in another indication. RESULTS: The PET/CT images of 18 women with known (n = 15) or suspected (n = 3) endometriosis were analyzed. Based on clinical follow-up and results of other imaging, biopsy, and/or postsurgical histology, the presence of lesions of endometriosis at the time of (18)F-FDG PET/CT was confirmed in 13 of 18 patients (72%). The per-patient positivity rate of (18)F-FDG PET/CT was 8/18 (44%; 95% confidence interval, 22%–69%). The patient-based detection rate of (18)F-FDG PET/CT in patients with confirmed lesions of endometriosis was 8/13 (62%; confidence interval, 32%–86%). On per-lesion/site basis, (18)F-FDG PET/CT detected 11 of 20 sites (55%) of endometriosis. The SUVmax of these lesions/sites ranged between 1.8 and 5.3 (median, 3.8). In 9 of 18 patients (50%), a total of 13 non–endometriosis-related lesions/sites were detected by (18)F-FDG PET/CT; their SUVmax ranged between 2.7 and 23 (median, 9.4). CONCLUSION: The interference of known or suspected endometriosis in reporting (18)F-FDG PET/CT performed in another indication was limited but possible and should be kept in mind, even in postmenopausal women, as the oldest patient with (18)F-FDG–positive endometriosis was aged 63 years. The lesions of endometriosis showed inconstant (18)F-FDG uptake with overlap of SUVmax with low-grade malignancies. In our series, the greatest SUVmax value of lesion of endometriosis was 5.3, somewhat higher than the threshold of 4 previously proposed for identification of malignant transformation of endometriosis.